S4S

S4S lumber means it is Surfaced Four Sides. It refers to standard dimensioned lumber such as  1×2, 1×6 and so on

Lancashire is a stocking S4S dealer of

Maple – 1×2, 1×3, 1×4, 1×5, 1×6 and 1×8 in various lengths

Red Oak – 1×2, 1×2 ¼, 1×3, 1×4, 1×5, 1×6, 1×8, 1×10 and 1×12 in various lengths